A philosophical question though: Is the point to remove only the post-formatted posts actually visible on the page from the main stream, while leaving in older post-formatted posts that had "fallen off" the widget?

Using this on my site currently, I'd expect the main stream not to show the post-formatted posts if the widget for that post format exists at all.

What about changing up the function to, instead of excluding specific post IDs that are on display, we add a $query->set based on the formats present using the NOT IN operator, which would exclude all posts of a specific format if displays via the widget?

My last pitch for a possible change in thought, using myself as the test case.

On ​http://bjk.staging.wpengine.com currently (at r25639 with .2 patch applied), I took a stream of image posts in one day. The latest one is in the widget, which happens to be at the bottom of the right sidebar.

The first two posts in the "main" area are the 2nd and 3rd most recent image format posts. It seems wonky to me that the most recent image would be in the sidebar, relatively buried by choice, while the older image formatted posts are in the main stream, more prominent in this case.

For my purposes, I want the main stream to be only the content formats that isn't relegated to the widgets. My longform posts are the highlight of the blog (as was before this patch, currently up at ​http://www.brandonkraft.com/), while my photoblog, random asides, etc are at /type/images, /type/asides, etc.

If I wanted the format to be part of the main stream, I wouldn't have limited it to display only the most recent in the widget. Or, at least taking the original functionality more into account, the most recent image in the sidebar while older content of the same format is promoted in a higher place potentially.

My last pitch for a possible change in thought, using myself as the test case.
...
My final pitch. :-)

Never stop fighting!

I think I was a bit too quick in my reaction. We narrow the results only down when we are on the front page, not on any subsequent page. I think does kind of make sense take all posts of that format out, to avoid showing older posts of the same format more prominently than newer posts.

Having said that, the purpose of the widget is to bring formatted posts to the reader's attention that would otherwise be hidden in subsequent pages. One could also argue to not remove the posts in the first place.